Control moment gyroscopes (CMG) are devices used for attitude control, and often form part of an attitude control system (ACS) in space vehicles. ACS's can be used for maintaining a particular fixed orientation of the vehicle with respect to some desired datum, or for changing the attitude of the vehicle when required.
For example, CMG's are reportedly used in DigitalGlobe's Worldview-1 and Worldview-2 satellites, and in the International Space Station. For example, Astrium and Rockwell Collins Deutschland provide CMG's for small satellites.
CMG's generally include a rotor spinning about an axis, while a gimbal tilts the rotor about a gimbal axis to change the direction of the angular momentum of the rotor. A gyroscopic torque is generated that results in the vehicle rotating, thereby changing its attitude. A controllable motor controls the tilt provided by the gimbal, and the speed of rotation of the rotor can be unchanged during tilting.
Some CMG's include a pair of gimbals to allow tilting about two orthogonal axes. Some CMG's spin the rotor at constant speed, while others spin the rotor at variable speeds, particularly during tilting of the rotor and are referred to as variable speed CMG's (VSCMG's).
References considered to be relevant as background to the presently disclosed subject matter are listed below:
U.S. Pat. No. 3,741,500 discloses an attitude control system for providing control torques on a vehicle, such as a space satellite, using four single gimbal control moment gyroscopes. The relatively simple constant-gain steering law permits three axis control after failure of any one of the four control moment gyroscopes.
U.S. Pat. No. 6,047,927 discloses control moment gyros in an array are rotated to reorient a satellite by an attitude signal. If the signal causes a gyro to have position that will produce a singularity in attitude control, a disturbance is introduced into the signal to avoid the singularity.
U.S. Pat. No. 8,014,911 discloses methods and systems for reorienting an agile vehicle, such as a satellite or spacecraft, using a control moment gyroscope (CMG) array. The CMG array comprises a plurality of CMGs onboard the agile vehicle. A disclosed method comprises obtaining an input torque command for reorienting the vehicle using the CMG array and, when the angular momentum of the CMG array violates or is approaching a momentum boundary criterion, decreasing the input torque command in the kinetic momentum direction, resulting in a modified torque command, and operating the CMG array using the modified torque command.
Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.